Equivalent C++ to Python generator pattern

Question

I\'ve got some example Python code that I need to mimic in C++. I do not require any specific solution (such as co-routine based yield solutions, although they would be acce

Answer 1

In C++ there are iterators, but implementing an iterator isn't straightforward: one has to consult the iterator concepts and carefully design the new iterator class to implement them. Thankfully, Boost has an iterator_facade template which should help implementing the iterators and iterator-compatible generators.

Sometimes a stackless coroutine can be used to implement an iterator.

P.S. See also this article which mentions both a switch hack by Christopher M. Kohlhoff and Boost.Coroutine by Oliver Kowalke. Oliver Kowalke's work is a followup on Boost.Coroutine by Giovanni P. Deretta.

P.S. I think you can also write a kind of generator with lambdas:

std::function generator = []{
  int i = 0;
  return [=]() mutable {
    return i < 10 ? i++ : -1;
  };
}();
int ret = 0; while ((ret = generator()) != -1) std::cout << "generator: " << ret << std::endl;

Or with a functor:

struct generator_t {
  int i = 0;
  int operator() () {
    return i < 10 ? i++ : -1;
  }
} generator;
int ret = 0; while ((ret = generator()) != -1) std::cout << "generator: " << ret << std::endl;

P.S. Here's a generator implemented with the Mordor coroutines:

#include 
using std::cout; using std::endl;
#include 
using Mordor::Coroutine; using Mordor::Fiber;

void testMordor() {
  Coroutine coro ([](Coroutine& self) {
    int i = 0; while (i < 9) self.yield (i++);
  });
  for (int i = coro.call(); coro.state() != Fiber::TERM; i = coro.call()) cout << i << endl;
}